Mount Prospect, Illinois 7 Day Weather Forecast

Wx Forecast - Wx Discussion - Wx Aviation

697
FXUS63 KLOT 090842
AFDLOT

Area Forecast Discussion
National Weather Service Chicago/Romeoville, IL
342 AM CDT Thu Jul 9 2026

.KEY MESSAGES...

- Scattered thunderstorms are expected at times through this
  evening. These storms will be capable of locally heavy
  rainfall which may lead to flooding, particularly if they
  stall or redevelop over areas hardest hit from last weekend.

- The strongest storms will also be capable of gusty to locally
  damaging wind gusts this afternoon and evening, greatest
  threat south of I-80.

- Mainly dry and warmer weather is expected this weekend into
  early next week.

&&

.DISCUSSION...
Issued at 342 AM CDT Thu Jul 9 2026

The earlier complex of thunderstorms approaching from eastern
IA/southwest WI has mostly eroded with only a few areas of rain
remaining. Not currently expecting any additional lightning
through the remainder of the overnight hours with this activity
but will still have to keep an eye on the remnant MCV moving
into northwest Illinois but it should move out over the lake
already by 7-8 AM. Earlier warm advective showers southwest of
the metro managed to produce a few lightning strikes but have
since decreased in coverage. Still can`t rule out a few spotty
showers south of the Kankakee River Valley through daybreak.

Attention then turns to a second MCV moving across central
Iowa. This feature is expected to progress east toward the area
through mid morning. Concerns are that this could lead to an
earlier "first round" of isolated to scattered showers and
thunderstorm development from mid morning through early
afternoon (30-40 percent chance). Forecast soundings show a
largely uncapped environment here locally already after 9-10 AM
so any forcing for ascent (such as with an MCV) would support
thunderstorm development. Model guidance has been struggling
with handling these smaller scale mesoscale features and have
based the first 12 hours of the forecast largely on radar,
satellite, and observational trends.

As the aforementioned MCV begins to shift southeast out of the
area toward mid-late afternoon, additional thunderstorm
development may then occur within the vicinity of a residual
outflow boundary or convergence axis situated across northern
and northeast Illinois. Exactly where this boundary ends up as
well as what the coverage of showers/storms will be remains
lower confidence, at least initially given a potentially slower
arrival of the parent mid-level vort/wave (which is still out
over northern NE/southern SD). Suspect that coverage may remain
more isolated to widely scattered during the afternoon until the
wave arrives leading to increasing coverage during the evening
(potentially still over portions of the Chicago metro) before
gradually shifting south and east and out of the area overnight.

The primary hazard with any thunderstorms today (from mid
morning through this evening) will be localized heavy rainfall.
PWATs in the upper end of climatology (2"+) will be supportive
of instantaneous rainfall rates in excess of 1-2"/hr. Given the
increased susceptibility for flooding in many areas after last
weekend`s multiple rounds of heavy rainfall, will continue to
message the localized threat of flooding. In spite of generally
weaker shear, precip loaded downbursts will remain possible with
the strongest storms which could produce strong to locally
damaging wind gusts (40-60 mph). The greatest threat (and level
1 out of 5 threat for severe weather) is greatest for areas
well south of I-80 but can`t fully rule it out areawide.

In the wake of our showers and storms a backdoor cold front is
expected to move inland off Lake Michigan late in the evening.
This may bring a period of fog and/or very low clouds across
much of the metro through early Friday morning, some of which
could end up locally dense. Something to keep an eye on with
later forecasts.

Looking ahead to Friday, additional convectively augmented
shortwaves are expected to move across the Mid-Mississippi and
Ohio Valley regions. Think that the majority of the shower and
storm coverage with these features will remain largely south of
the area but have maintained 20-40% chances for areas south of
a Peru, IL to Rensselaer, IN line in case they end up a bit
farther north.

While a few diurnally driven showers can`t be ruled out on
Saturday, upper level ridging expands across the central CONUS
over the weekend into early next week which should lead to
mainly dry conditions into the first part of next week with
temperatures in the upper 80s to around 90. Given we will be on
the northeast periphery of the ridge we will have to monitor the
potential for thunderstorm complexes rounding the ridge across
the broader region toward midweek.

Petr

&&

.AVIATION /06Z TAFS THROUGH 12Z FRIDAY/...
Issued at 100 AM CDT Thu Jul 9 2026

Forecast concerns for the terminals...

- 20-30% chance for isolated showers early Thursday morning,
  mainly near RFD.

- Scattered showers and thunderstorms expected Thursday
  afternoon and evening. Any of which could result in localized
  heavy downpours and reduced visibility.

- MVFR ceilings Thursday night into Friday morning with
  potential for patchy fog after midnight.


A busy weather and complicated TAF period ahead as several
disturbances will be pivoting through northern IL and northwest
IN. Prior to the arrival of the disturbances, increasing VFR
clouds are expected tonight with light southwest winds that will
become more westerly by Thursday morning. As we head into
Thursday morning, the line of decaying line of showers and
embedded thunderstorms (currently in IA and southwest WI) will
be moving through northwest IL. With radar continuing to show
these showers eroding suspect that mostly dry conditions will
prevail through Thursday morning, but with an embedded
convectively enhanced low being noted within the showers cannot
fully rule out some isolated showers developing around daybreak
and lingering through the morning (20-30% chance). Due to the
lower confidence on coverage of any morning activity have opted
to maintain VCSH at all TAFs with a PROB30 at RFD where
confidence is slightly higher that something could materialize.

Regardless of what develops Thursday morning, scattered showers
and thunderstorms are expected to develop along the outflow
boundary from tonight`s storms that should be draped over
northern IL. While exact timing as to when the afternoon
activity will kick off remains uncertain, latest forecast
guidance trends seem to be leaning towards a 21-22z initiation
with thunderstorms likely to persist through at least 01-02z as
the boundary slowly drifts south through the terminals. Though,
there is a chance that some showers could linger through the
evening especially if the boundary is slower than forecast. For
now have opted to maintain the broad VCSH mentions with targeted
PROB30s for the better thunder windows at each location. Any
showers/storms this afternoon will be capable of producing
locally heavy downpours which would result in IFR visibilities
and possibly even some ponding issues particularly near the
saturated areas from last week`s rains.

Showers and storms should taper after 03z as the boundary drifts
south and the associated disturbance pivots east of the area. In
the wake of the boundary a northeast wind shift will occur with
speeds initially around 8-10 kts but those will be waning to
around 5 kts after midnight. Ceilings will also lower to MVFR
behind the boundary where they look to remain for the rest of
the forecast period. While there is a signal for some IFR
ceilings as well, confidence on their coverage is low so have
opted to handle with a SCT012 mention for now. Furthermore,
there is also a decent signal for patchy fog to develop near
Lake Michigan and ooze inland overnight some of which could be
locally dense. At this time the 30-hour TAFs will have a 6SM BR
mention to tease the fog, but more refined TEMPOs may be needed
for lower visibilities as confidence grows.

Yack

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...None.
IN...None.
LM...None.

&&

$$

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